This invention relates to a preparation process of a 2-hydroxy-3-alkoxypropylglyceryl ether or the like, and more specifically to a preparation process of a 2-hydroxy-3-alkoxypropylglyceryl ether represented by the general formula (IV): ##STR1## wherein R represents a saturated or unsaturated, straight or branched chain, aliphatic hydrocarbon group having 8-24 carbon atoms (may be abbreviated as ".alpha.-monoalkyl ether of diglycerol" later in the present specification) and its synthetic intermediate, 4-(2'-hydroxy-3'-alkoxy)propoxymethyldioxolane represented by the general formula (III): ##STR2## wherein R.sub.1 and R.sub.2 are individually a hydrogen atom or a lower alkyl, aryl or aralkyl group (may hereinafter be abbreviated as "1,3-dioxolane compound").
In the natural world, there are a number of polyalcohol derivatives containing one or more ether bonds, among which monoalkyl ethers of glycerol (called "glyceryl ethers") are particularly well-known. For example, fish lipid contains palmityl glyceryl ether (chimyl alcohol), stearyl glyceryl ether (batyl alcohol) and oleyl glyceryl ether (selachyl alcohol).
These glyceryl ethers have found wide-spread commercial utility, particularly, as cosmetics bases and the like owing to their W/O-type emulsification characteristics (see, for example, Japanese Patent Laid-open Nos. 87612/1974, 92239/1974 and 12109/1977). Besides, it has been known that they have pharmacological effects such as erythropoietic stimmulating effect for bone marrow, antiinflammatory effect and antitumor activities (see, Japanese Patent Publication Nos. 10724/1974 and, especially, 18171/1977).
Taking into consideration that such glyceryl ethers are unique surfactants having many characteristic features, many attempts have been made to derive polyol ether compounds having a molecular structure analogeous to those of glyceryl ethers (in other words, containing one or more ether bonds and hydrophilic OH-groups therein) from polyalcohols (see, for example, U.S. Pat. No. 2,258,892; Japanese Patent Publication No. 18170/1977 and Japanese Patent Laid-open Nos. 137905/1978 and 145224/1979). The thus-obtained polyol ether compounds are used as cosmetics bases (see, West German Patent Laid-open No. 2,455,287) and general emulsifiers (owing to their W/O-type emulsification characteristics) and also as antimicrobial and fungicidal agents.
As preparation processes of such polyol ether compounds, there have heretofore been known, roughly divided, the following three types of preparation processes:
(1) A polyalcohol is reacted in the presence of an acid or basic catalyst with an alkyl glycidyl ether (I);
(2) An alkali metal alcoholate is formed from a polyalcohol (VI) in the presence of an alkaline substance and the resultant alkali metal alcoholate is reacted with an alkyl halide or the like; and
(3) An alcohol (VII) is reacted in the presence of an acid or basic catalyst with an epoxide compound (V) of the 1,3-dioxolane type and the resultant addition product (III') is subjected to hydrolysis (see, Journal f. Prakt. Chemie, Band 316, 325-336 (1974)).
The above processes may be represented by the following chemical equations: ##STR3## wherein, X represents a halogen atom and R has the same meaning as defined above.
However, these conventional processes are accompanied by the following drawbacks, whereby making it extremely difficult to selectively produce polyol ether compounds in an industrial scale:
(a) First of all, there may be mentioned the extremely poor selectivity of the reaction in each of the processes. Thus, the yield and purity of the intended compound (IV) are limited to extremely low levels in the overall reaction products, whereby deleteriously affecting its physical and chemical properties and making it difficult to provide the intended compound (IV) of uniform quality. The processes (1) and (2) produce, besides the intended ether compound (IV), position isomers of the monoalkyl ether and a mixture which comprises ether compounds substituted by various numbers of alkyl groups such as dialkyl ether and trialkyl ether, because the polyalcohol contains many reactive primary and secondary OH-groups in the same molecule (for example, glycerol in the reaction formula (1) contains two primary OH-groups and one secondary OH-group while diglycerol in the reaction formula (2) has two primary OH-groups and two secondary OH-groups) and these OH-groups may individually take a part in the reaction substantially at the same velocity.
Hence, it is necessary to go through another step such as distillation in order to isolate the intended compound from the reaction product mixture, leading to an irksome process and preventing its adoption in an industrial scale. The process (3) yields, on the other hand, many by-products in addition to the intended addition product (III') due to occurrence of many side reactions, whereby leading to a drawback that its selectivity is considerably lowered. The present inventors attempted to confirm the structure of an .alpha.-monoalkyl ether of diglycerol according to this invention, by preparing the ether in accordance with the process (3). As a matter of fact, the intended addition product (III') was obtained with an extremely low yield, i.e., about 30% where a basic catalyst was employed and about 35% or so when an acidic catalyst was used (see, Comparative Examples 3, 4 and 5);
(b) To improve the selectivity of the reaction mentioned in the above item (a), some measures have been taken including using the polyalcohol or monoalcohol excessively or using a special polar solvent to keep the reaction system uniform. However, the incorporation of such measures in an industrial scale is certainly impractical because it is necessary to recover and recycle the polyalcohol used excessively and the use of such a special polar solvent leads to a higher production cost and involves difficult handling of the same; and (c) in order to isolate the intended compound (IV) from the mixture as mentioned in the above item (a), it is contemplated to, in addition to the distillation, protect any free OH-groups through a chemical reaction, separate and collect the thus OH-protected compound and then to remove the protecting groups. However, this results in an increased reaction steps or a cumbersome and complex process. It is thus difficult to practice such a process in an industrial scale.